The present invention relates to a method of galvanizing a piece of arbitrary shape and size, and in particular to a method of galvanizing part of such a piece.
Galvanization is a technique presently used in numerous industries and it enables pieces to be obtained having a chromium-titanium- or gold-plated appearance, for example. Galvanization is essentially an electrolytic reaction whereby a metallic salt is deposited on a metal, generally in order to preserve it from oxidation. Galvanizing a piece thus makes it possible to obtain an appearance that is metallic and non-oxidizable.
Galvanized pieces are not necessarily themselves made of metal, but they can be made of some other material, e.g. a plastics material, for reasons of expense and ease of obtaining particular shapes. Plastics materials are of low cost and easy to work, so pieces can be obtained having all kinds of shapes, in particular by using the known techniques of injecting the plastics material into a mold. Various families of plastics materials can be used for injection molding, such as polycarbonate (PC), polyethylene terephthalate (PET), or acrylonitrile butadiene styrene (ABS), for example. In addition, certain families of plastics can be galvanized, such as ABS for example, while others cannot, such as PC, for example.
Thus, galvanizing pieces made of plastics material represents numerous applications in a variety of industries, such as the automobile industry, the industry providing radio communications terminals or personal assistants, or any other industry where it is necessary to give a non-oxidizable metal-plated appearance to a piece that is made of plastics material.
Galvanizing a plastics material piece essentially requires the following steps to be performed: dipping the piece in a chemical acid bath which etches the surface of the plastics material and creates cavities in the surface of the piece; and then dipping the piece in succession in a plurality of metallic baths serving firstly to deposit metals (e.g. copper and/or nickel) into the surface cavities of the plastics material, and secondly to perform galvanization proper by depositing metallic salts which react electrolytically with the previously deposited metal. The baths of metallic salts can be based on chromium, titanium, or gold, for example, depending on the final appearance required for the galvanized piece.
Depending on requirements, techniques, or taste, it can be advantageous for a given piece to present an appearance that is not metallic in part, e.g. that has the appearance of a plastics material, and that is metallic in part, i.e. it can be preferable for a single piece to be galvanized in part only.
Various techniques for partially galvanizing pieces have already been proposed in the prior art. A first technique, shown in FIG. 1, consists in making a piece 10 out of a galvanizable material 11, and in using a mask 50 that leaves apparent only those zones which are to be galvanized, after which the piece 10 is dipped in the galvanizing baths 30. A second technique, illustrated in FIG. 2 and described for example in patent application EP 0 256 482 A2, consists in making a piece 10 out of at least two distinct materials 11 and 12, one of which is galvanizable (material 11) while the other is not (material 12), with the piece advantageously being made by a dual injection method in a suitable mold. The entire piece is then dipped into the galvanizing baths, but only one type of material 11 is etched by the acid and thus galvanized by the metallic baths 30.
Those techniques known in the prior art present numerous drawbacks. The use of a mask adds a step to the method of manufacturing the pieces, and that can be penalizing in large-volume production. In addition, it is necessary to provide fixing points for the mask on the piece that is to be galvanized, and this can be detrimental to the overall appearance of the piece and can present difficulties for pieces that are small in size.
The dual injection technique is made complex by the need to handle two different materials. In addition, the molds used for dual injection are much more complex than those used for injecting using a single material only.
However, partial galvanization, in particular of pieces made of plastics material, is becoming increasingly widespread, particularly in industries that use design as a selling technique. It enables pieces to be made using materials that are of low cost, said pieces presenting surface portions that are metallic in appearance (e.g. chrome-plated) that are continuous with surface portions having the appearance of plastics materials.
The invention can thus be applied to a radio communication terminal, such as a mobile telephone or a personal assistant, comprising a shell of plastic material that is galvanized in part only. The invention can also be applied to a plastics material motor vehicle piece that is galvanized in part only.
The ability to galvanize a single piece of plastics material in part only is thus of great interest. The invention provides such a method, while avoiding the drawbacks of the prior art.
More particularly, the present invention provides a method of partially galvanizing a piece obtained by injection molding, the method comprising the following steps:
inserting a film in a mold;
injecting a galvanizable material into the mold;
unmolding the piece; and
galvanizing the entire piece;
said film being made of a material that is not galvanizable and that adheres strongly to the injected galvanizable material.
According to an advantageous characteristic, the method of the invention includes a step of coloring and/or printing the film prior to inserting it in the mold.
In various embodiments, the film is printed by silkscreen printing or by ink jet printing.
In various embodiments, the film is printed on the outside face of the film, or else on the inside face of the film, i.e. its face which comes into contact with the injected material, said film then being constituted by a material that is transparent.
In various embodiments, the film is of polycarbonate (PC), of polybutylene terephthalate (PBT), or of polymethyl methacrylate (PMMA).
According to a characteristic, the galvanizable material injected into the mold to constitute the piece is a plastics material, advantageously acrylonitrile butadiene styrene (ABS), or acrylonitrile butadiene styrene/polycarbonate (ABS/PC).
The invention also provides a piece made of a galvanizable material having a portion of its visible surface galvanized, wherein the non-galvanized portion of its visible surface is covered in a film of non-galvanizable material that adheres strongly to the galvanizable material constituting the piece.
According to a characteristic, the film covering the non-galvanized visible portion of the surface carries decoration.
In various embodiments, the decoration is coloring and/or printing.
According to a characteristic, the partially galvanized piece is made of a plastics material, advantageously of acrylonitrile butadiene styrene (ABS), or of acrylonitrile butadiene styrene/polycarbonate (ABS/PC).
In a particular application, the invention provides a radio communications terminal comprising a shell whose outside surface is galvanized in part, wherein the non-galvanized portion of the surface of the shell is covered in a film of non-galvanizable material that adheres strongly to the material constituting the shell.